I'm new to this, but I really feel like I need to share a $20 trick for awesome improvements for in-car-video sound.
Good sound is key to good video, and it's not hard or expensive to do. In-camera sound is generally terrible, and while the Hero3 is a big improvement for action cams, it still sucks. The pros shoot with dedicated sound recorders. The Zoom H1 is a great solution at $100, but that's a lot for informal videos and requires syncing in an editing program.
If your camera has an external mic input, an easy, light, and cheap way to get better sound is by using a lavalier microphone. The frequency sensitivity lends itself well to engines, and their long cables let them work anywhere in or around your car.
The ones I picked were the Audio Technica ATR-3350, which is $17-18 online. It has a foam windscreen, you should wrap it in some more soft foam if you have it directly in the airstream.
If you want stereo, you can get one of these buggers. The female jacks are right and left mono, the male plug is a stereo plug. No mixing board needed.
To relieve stress on the camera's microphone jack, I use a 6" right angle extension cable and tape the female end somewhere close to the camera.
When recording stuff quieter than engines, you might start to hear a bit of baseline noise from the camera itself (which is why a dedicated recorder is a good step up). A way that I found to eliminate this is to boost the signal from the lavaliers. There are companies that make tiny battery-powered amplifiers for headphones, which happen to amplify stereo signals in the exact manner we need. These are cheap ($6) and nearly eliminate noise in the circuit. The Fiio E3 is a good start. The Hero cams have automatic gain control and handle volume changes pretty well.
Here are some samples, keep in mind that I've just started with this.
http://www.youtube.com/watch?v=W1cx6z8YSdY
Anything in-car here: http://www.youtube.com/watch?v=8F0zFgiRFEw#t=32s
Anybody have any similar tricks or useful tips?
